The size and construction of powerboats are governed by the international U.I.M. which has established classes related to engine size and length. Class I boats, where most of my experience lies, can have a maximum length of 4.5 feet and power is limited to petrol engines of up to 16 litres. The speeds of the fastest boats are in the region of 85 m.p.h. with full fuel on board, increasing to around 90 m.p.h. at the end of the race. Over a ton of aviation spirit is carried as fuel. This speed can only be fully utilized in fairly calm conditions. Trim tabs on the transom and a jack for the stern drive units help the driver to keep the boat on the water.